Take the mass of half a million Earths and compress it down to the size of Manhattan. If you have taken precaution and survived the energy release from this process, then well done! You’ve got yourself a neutron star, one of the densest objects in the universe.

Under certain conditions neutron stars are not just the smallest and densest stars out there, they can also be "magnetars" – the strongest magnets in the universe. Now, for the first time, astronomers have spotted one of these magnetars surrounded by a wind nebula.

The object is called Swift J1834.9-0846, or J1834.9 for short, and astronomers think it's associated with the W14 supernova remnant. Neutron stars form in powerful supernova explosions, which also create large clouds of materials. These are pushed and slowly eroded by the energetic light and particles from the stars, and so they are nicknamed wind nebulae.

"Right now, we don't know how J1834.9 developed and continues to maintain a wind nebula, which until now was a structure only seen around young pulsars," said lead researcher George Younes, a postdoctoral researcher at George Washington University in Washington, in a statement.

Wind nebulae, like the famous crab nebula, glow from the streams of particles emitted from the neutron star, which can spin hundreds of times per second. Some of this rotational energy is spent to produce light and the powerful stream of particles.

"If the process here is similar, then about 10 percent of the magnetar's rotational energy loss is powering the nebula’s glow, which would be the highest efficiency ever measured in such a system," Younes continued.

Magnetars have magnetic fields millions of times stronger than any man-made magnet, but their origin is still unclear. Out of about 2,600 neutron stars known, astronomers have detected only 29 magnetars.

Magnetars don’t continuously produce light and particles but produce huge outbursts when the magnetic field reconfigures to a lower-energy state. The fact that a wind nebula survived many of these is incredible and the details are reported in a paper that will be published in the Astrophysical Journal.

"The nebula around J1834.9 stores the magnetar's energetic outflows over its whole active history, starting many thousands of years ago," said team member Jonathan Granot, an associate professor in the Department of Natural Sciences at the Open University in Ra'anana, Israel.

"It represents a unique opportunity to study the magnetar's historical activity, opening a whole new playground for theorists like me."

^{This X-ray image shows extended emissions around a source known as Swift J1834.9-0846, a rare ultra-magnetic neutron star called a magnetar. ESA/XMM-Newton/Younes et al. 2016}